This invention relates to the control of fuel cell power plants, and more particularly to the control of multiple fuel cell power plants at a site. More particularly still, the invention relates to the control of multiple fuel cells at a site to provide a distributed resource in a utility grid.
Individual fuel cells have been used both experimentally and commercially in various configurations to power various electrical loads. In the main, the applications have relied on a single fuel cell, or fuel cell power plant, to supply electrical power to one or more loads at the site. While such sites may be mobile, as in the powering of the electric drive motor of a vehicle, in the main they are large and stationary. These applications have typically been individual commercial installations or buildings, perhaps involving computers or similar electronic data processing equipment or medical equipment requiring a reliable source of power.
To operate such fuel cell power plants, there are normally associated various controls for the direct control of the fuel cell itself and its production of DC electrical power, as well as additional controls for converting the DC power to AC power, for connecting and disconnecting power with the loads, etc. In some instances, the fuel cell power plant is connected to the loads in parallel with the normal electric utility grid, and may act in lieu of, or in addition to, the grid to supply power to the loads. In other instances, there may be multiple fuel cell power plants at a site, collectively connected to the loads in parallel with the utility grid. However, even in such configuration, the control of the fuel cells has typically been on an individual basis, with little or no provision for an integrated control arrangement to optimize the use of multiple fuel cell power plants interconnected with the utility grid and the loads.
When one or more fuel cell power plants are connected to the utility grid as well as the loads, they are said to be in a grid connected (GIC) configuration or mode. Alternatively, when those fuel cell power plants are connected only to the loads, they are said to be in grid independent (G/I) mode. In the G/I mode, the fuel cell power plants typically follow the load and apportion the load among the power plants. The transition from one such mode to the other, and the control of multiple fuel cell power plants relative to the loads present additional control complexities that have impeded the efficient and economic utilization of multiple fuel cell power plants as distributed resources in electric utility grids.
Accordingly, it is an object of the invention to provide a control arrangement for the efficient and economic utilization of multiple fuel cell power plants at a site as a distributed resource in a utility grid.
It is a further object of the invention to provide a control arrangement to optimize the interrelationship between multiple fuel cell power plants and multiple loads at a site in order to enhance utilization of the plants as a distributed resource in a utility grid.
It is a still further object to provide a control arrangement for a multiple fuel cell power plant generation system at a site that coordinates operation of the fuel cell power plants in an integrated, or unified, manner in both the G/C and the G/I modes of operation.
The present invention concerns the control of multiple fuel cell power plants at a site, particularly as a distributed resource for inclusion in a utility grid. The invention further concerns the unified, or integrated, control of multiple fuel cell power plants at a site, both in a grid connected (G/C) mode to facilitate their use as a distributed resource in a utility grid network and in a grid independent (G/I) mode to optimize their value and utility as an/the independent power supply to one, or typically multiple, customer loads at the site.
Accordingly the present invention relates to a fuel cell-powered generating system at a site for inclusion as a distributed generating resource in a distributed generation utility power grid, and comprises multiple fuel cell power plants at the site, at least one, and typically multiple, loads located substantially at the site, and a site management system operatively connected to the multiple fuel cell power plants, the one or more loads, and the utility grid for controlling the fuel cell power plants in an integrated, or unified manner, in, alternatively, a grid connected mode of operation having the fuel cell power plants connected to the load(s) and to the power grid, and a grid independent mode having the fuel cell power plants connected to the load(s) independent of connection to the power grid. This integrated control provided by the site management system allows the utility to view the multiple fuel cell power plants at the site as a single, or unified, distributed generating resource when connected to the grid. Accordingly, as used in this context, the terms xe2x80x9cintegratedxe2x80x9d and xe2x80x9cunifiedxe2x80x9d are viewed as being substantially synonymous. Moreover, the integrated control facilitates the operation of the site in the G/I mode where the fuel cells are typically load-following and have operated independently of one another. In this latter regard, the integrated control in the G/I mode further facilitates a load management (sharing and shedding) capability for assuring power to critical loads.
The fuel cell power plants each include control and logic capabilities for folding back (reducing) rated power levels to lesser levels, if necessary, in response to various power plant conditions, and for providing signals representative of the instant power level capability of the respective plants. As used herein in association with power capacity and load demand, the term xe2x80x9cinstantxe2x80x9d is intended to be synonymous with xe2x80x9cpresentxe2x80x9d, xe2x80x9ccurrentxe2x80x9d, or xe2x80x9cinstantaneousxe2x80x9d. The site management system sums the individual power capacities of the respective fuel cell power plants and obtains a measure of the total instant power capacity of the multiple power plants at the site. This measure of total power capacity and the respective individual power capacity measures are used to provide a site power measure to the utility grid and to appropriately load each of the power plants in G/C mode, and are used in the G/I mode to appropriately load each of the power plants to operate in a unified manner and further, for a load shedding function. In this latter regard and assuming multiple loads, the site management system is operative to recognize the instant load demand, the instant total power capacity, and a predetermined prioritization of the loads in the event load demand exceeds instant total power capacity, and to selectively shed or disconnect loads in accordance with the schedule, if necessary.
The site management system includes at least one, and typically several, signal processing logic controllers cooperatively interacting with one another, the multiple fuel cell power plants, and the utility grid to perform the integrated control functions of the invention.
The foregoing features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof as illustrated in the accompanying drawings.